In a normal pumping well, an oil pump is connected to the lower end of the oil well pipe string and sucker rods connected to the pump pass up through the pipe string to connect to a polished rod passing through a three-way fitting. The lower coupling of this fitting connects to the upper end of the pipe string and the axially aligned upper coupling receives a stuffing box through which the polished rod extends to connect through an appropriate clamp and carrier bar to a bridle. The bridle in turn is reciprocated upwardly and downwardly by a structure referred to in the art as a "horsehead". The lateral outlet of the three-way coupling connects to an oil flow line so that oil pumped up from the bottom of the well through the pipe string can be collected in this flow line. The stuffing box prevents oil leakage around the polished rod as it is reciprocated up and down.
In certain circumstances, the polished rod can become disconnected or break resulting in its being ejected from the stuffing box. The pumped oil under pressure will then pass up through the stuffing box and cause a substantial mess in the surrounding area not only irritating to environmentalists but involving substantial clean-up expenses.
While it is common practice to provide a Radigan type close-off valve between the lower coupling of the three-way fitting and upper end of the pipe string, such valve must be manually closed and during the period of closure, substantial amounts of oil can escape through the stuffing box.
To overcome the foregoing problem, there are available blow-out preventers arranged to be inserted above the stuffing box connecting to the upper coupling of the three-way fitting, the polished rod passing through this blow-out preventer. Essentially, the structure includes a spring biased ball bearing against the rod in such a manner that if the rod breaks and is ejected, the ball is free to seat up against a valve seat in the blow-out preventer thereby blocking passage of oil up through the stuffing box to the exterior.
The problem with the foregoing types of blow-out preventers is that the height of the well head structure itself is necessarily increased in order to insert the blow-out preventer above the upper stuffing box and the normal three-way fitting. This increased height can cause difficulties with respect to the remaining pumping components in that the distance between the exit point of the polished rod from the upper stuffing box to the carrier bar and bridle assembly is decreased. There is thus necessitated some repositioning of components involved when such blow-out preventers are used.
Another problem with such blow-out preventers is the fact that they are relatively expensive items, this expense resulting from the necessity of providing an appropriate seat for the ball which normally might take the form of an additional stuffing box.
There is a need, accordingly, for some type of blow out protection which will automatically operate should a polished rod break or be ejected from the normal stuffing box which will not only avoid any increase in height of the well head structure but also can be produced economically so that the expense to oil producers of such blow-out preventers can be reduced.